The genetic improvement of wheat for conditions of drought stress requires an evaluation of specific physiological attributes related to drought resistance, as a basis for developing a working screening procedure. An important component of drought resistance is dehydration avoidance. Dehydration avoidance is defined as plant ability to maintain a relatively higher leaf water potential under conditions of soil moisture stress. The purpose of this investigation was to document the existance of and variability in dehydration avoidance within a random sample of advanced and well‐adapted wheat ( Triticum sp.) genotypes. Midday leaf water potentials (Ψ 1 ), as a measure of dehydration avoidance, were monitored with a pressure chamber in the various wheat genotypes, simultaneously subjected to soil moisture stress in three different field tests. Leaf diffusive resistance (R 1 ) was monitored with a diffusion porometer in two of the tests. Genotypes varied significantly in their midday leaf water potentials. About 2 bars of Ψ 1 were sufficient to differentiate significantly between genotypes. Variations in Ψ 1 were greater than variations in R 1 among genotypes. The largest difference in Ψ 1 between extreme genotypes, as observed in these tests, reached 12.9 bars. In one test, where drought stress developed during the spike development stage, leaf water potential (but not leaf diffusive resistance) was correlated with the final number of grains per spike across genotypes of similar phenology. Linear regressions developed for each genotype between Ψ 1 and R 1 revealed large variations among genotypes in stomatal response to Ψ 1 . These relationships lead to the conclusion that dehydration avoidance in only a few of the genotypes may have resulted from stomatal sensitivity and closure at low stress levels. Most of the avoidant genotypes, however, maintained relatively open stomata.
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Blum et al. (1981) studied this question.